Website providers have a moral obligation to stop pupils posting offensive school videos that demean their teachers or other children, the education secretary said yesterday. Alan Johnson told teachers that companies had a responsibility to ensure their sites were properly policed to prevent young people putting humiliating clips taken by mobile phone cameras on the internet.

Addressing a conference of the NASUWT union in Belfast, Mr Johnson said such cyber-bullying was "cruel and relentless, able to follow a child beyond the school gates and into their homes". He added: "The online harassment of teachers is causing some to consider leaving the profession because of the defamation and humiliation they are forced to suffer."

New powers allowing teachers to confiscate mobiles being used maliciously in school would help, he said. "But there is a wider responsibility upon the providers of the sites which broadcast this material.

"These are big companies. They have a social and moral obligation to act. Without the online approval which appeals to the innate insecurities of the bully, such sinister activities would have much less attraction. I am therefore calling on the providers of these sites to block or remove offensive school videos in the same way as they have commendably cut pornographic content. By removing the platform we blunt the appeal."

However, Mr Johnson said the internet had been "an incredible force for good" in education. YouTube, one of the web providers that has drawn most complaints from teachers, said it "enables millions of young people globally to communicate with each other". But there was "a tiny minority that uploads content contrary to our guidelines". The company removed offensive material where appropriate.

Google urged heads to confiscate phones. "If teachers are concerned ... then the real question is why mobile phones are there at all," said a spokesman. Other companies have said making clear to children that any posting can be traced back to its source acts as a powerful deterrent.

Mr Johnson called for a "new 3Rs" of rules , responsibility and respect, backed up by new powers and guidelines to crack down on misbehaviour in and out of the classroom, including a right for teachers to use physical force to restrain or control aggressive pupils and a promise of tough action against children making false or malicious allegations against staff.

The guidance published by Mr Johnson's department yesterday also said classroom behaviour would be improved if pupils were praised and given special prizes. "Rewards are more effective than punishment in motivating pupils," it said. Mr Johnson also announced that an extra £110m would be spent over the next three years on upgrading the rebuilding specifications for 200 secondary schools to help them towards carbon neutrality.